Carbon black is used in large quantities for the coloration and pigmentation of many substrates due to its strong color and relatively low cost. Carbon black can be produced by a number of different processes, for example, furnace black-, channel black-, gas black- or other thermal oxidative processes.
Such carbon black products are often tailor made for specific applications like plastics, automotive solvent or waterborne based paints or inks. These products can be lacking in ease of dispersibility. Furthermore, these products show a strong absorption in the near IR region. Thus, articles colored by carbon black heat up quickly when exposed to sunlight, which is particularly problematic when used in car upholstery.
Another major drawback of carbon black is its color characteristics when used in different concentrations or in particular in combination with other organic, inorganic or effect pigments. Carbon black often tends to shift to an undesirable brownish hue. Thus, its use for certain color styling is limited.
Black colored cars are popular worldwide. They are painted mainly with carbon black pigments. The main drawbacks of such pigments are their high viscosity and often poor gloss behavior.
Black organic pigments are known. For example, German Patent No. 2,451,780 describes N-substituted perylene tetracarboxylic acid diimides as black pigments for paints, plastics and inks.
Many patents also describe the use of pigment mixtures for the creation of black colorations. For example, U.S. Pat. No. 6,235,106 describes blue shade black pigment compositions useful in paints, inks and plastics, comprising a mixture of iron oxide, chromium oxide and manganese oxide. The iron oxide primarily contains yellow iron oxide while the manganese oxide contributes to the strength and blueness of the pigment.
Published Japanese Patent No. 04-065,279 A2 describes lightfast black ink ribbons that are prepared from inks containing multiple light-resistant organic pigments. One such ink contains C.I. Pigment Yellow 123, C.I. Pigment Red 88, and C.I. Pigment Blue 15:6.
Published Japanese Patent No. 01-074,277 describes a method of toning carbon black containing inks to reduce their reddish tint by mixing them with Cu phthalocyanine pigments obtained by treating phthalic acid and/or its derivatives, urea, and Cu or its compounds in organic solvents in the presence of catalysts and benzophenone-3,3′,4,4′-tetracarboxylic acid, its anhydride, or imides.
Published Japanese Patent No. 10-104,599A describes a method for coloring resin compositions for forming shading film for liquid crystal displays—consisting of a combination of organic pigments having the color yellow, blue and purple or the combination of organic pigments with yellow, red and blue color.
U.S. Pat. No. 5,540,998 describes colorant compositions containing at least two of 1) a red pigment, 2) an orange pigment, 3) a yellow pigment, 4) a green pigment, 5) a blue pigment and 6) a violet pigment. Each of the pigments must exhibit a particular reflectance. The colorant composition is described as being an achromatic black formed by additive mixing. An additive mixture of Pigment Green 7, Pigment Yellow 154 and Pigment Violet 19 is exemplified in Table 1.
U.S. Pat. No. 6,010,567 describes black-pigmented structured high molecular weight material for black matrixes for optical color filters. The patent relates to a black-pigmented high molecular weight organic material that is structured from a radiation-sensitive precursor by irradiation. The pigmentation consists of colored organic pigments, at least one of which is in latent form before irradiation.
European Patent Application No. 23,318 describes gray to black colored thermoplastic film for laminated identity cards, containing white pigment and/or filler and a gray mixture of colored organic pigments. The film is specified for the production of laminates for identity, checks or credit cards. It has an inconspicuous appearance and strong covering power, making it especially useful for purposes where forgery needs to be made difficult, but is easily detected. Preferred materials are (A) Sb oxide, kaolin, silica, chalk, Ba sulphate, Ti dioxide and ZnS; (B) mixtures of red and green pigments in 6–12:10 weight ratio; violet and green in 5–15:10 weight ratio; and violet, yellow and blue in 20 to 30:10 to 50:60 to 10 weight ratios.
Other patents describe the surface treatment of carbon black to improve the pigment properties for application in coatings and inks.
For example U.S. Pat. No. 5,922,118 describes ink jet compositions comprising an aqueous vehicle and a modified colored pigment comprising colored pigment having attached at least one organic group, the organic group comprising a) at least one aromatic group or a C1–C12alkyl group, and b) at least one ionic group, at least one ionizable group, or a mixture of an ionic group and an ionizable group, wherein the at least one aromatic group or C1–C12alkyl group of the organic group is directly attached to the colored pigment and the organic group is present at a treatment level of from about 0.10 to about 4.0 micromoles/m2 of the colored pigment used, based on the nitrogen surface area of the colored pigment, wherein said colored pigment comprises carbon, anthraquinones, phthalocyanine blues, phthalocyanine greens, diazos, monoazos, pyranthrones, perylenes, heterocyclic yellows, quinacridones, (thio)indigoids and mixtures thereof. Such modified carbon products have better pigment properties when applied in ink jet systems, but they require sophisticated preparation procedures and therefore are uneconomical.
U.S. Pat. No. 5,962,574 describes a primer coating composition capable of protecting a substrate susceptible to degradation by ultraviolet light, said composition serving as a primary coat on said substrate beneath a multi layer color base coat/clear top coat finish. The UV light blocking pigments used are carbon black pigments surface modified with pigment derivative codispersant along with polymer dispersant. The pigment co-dispersant is a copper phthalocyanine derivative such as sulfonated copper phthalocyanine.
Sulfonated copper phthalocyanine can significantly improve the rheological properties of carbon black pigments when applied in conjunction with polymeric dispersants. However, sulfonated copper phthalocyanine has a very strong blue color and the addition of only small quantities can inopportunely shift the hue of the carbon black. Furthermore it is not sufficiently weather fast for employment in an automotive top coating, since the hue of such a coating can change quickly on exposure.
The state of the art offers various ways for the generation of black colors. However, no carbon black compositions are described that show universal pigment properties for an application in a choice of substrates, in particular topcoat automotive paint coatings.